X-ray system



y 1936- w.'K. KEARSLEY 08 XLRAY SYSTEM -Filed July 21, 1952 Fig. l.

Inventor: William K. Kearsley,

byW

His Attorney.

Patented May 5, 1936 UNITED STATES X-RAY SYSTEM William K. Kearsley,

Schenectady, N. Y.,. as-

signor to General Electric Company, a corporation of New YorkApplication July 21, 1932, Serial No. 623,760

7 Claims.

The present invention relates to the generation of X-rays and its objectis to provide an apparatus whereby high tension current through an X-raytube may be easily and instantaneously switched on and oiT.

My invention is particularly applicable to X- ray apparatus in whichcurrents of relatively high amperage are used for very short intervalsas in so-called instantaneous radiography for taking radiographs ofmoving objects. In order to reduce the size of transformers required tofurnish the current, such an apparatus may be provided with one or morecapacitors which are arranged to be discharged when a radiograph isdesired. The switching or control of a high voltage capacitor in anX-ray system presents difficulties of its own. My improved apparatusprovides for the control or switching on or off of large currentsequally as well when the energy is delivered by a capacitor as when itis delivered by a transformer, battery, or other form of supply device.

As will be hereinafter described in greater detail my improved apparatuscomprises an X-ray tube containing a control electrode, together withcircuit connections for charging said control electrode to a negativepotential whereby flow of current through the X-ray tube is inhibiteduntil desired. An arrangement is provided whereby the negative potentialmay be instantaneously released at the will of the operator, as by apushbutton switch thereby bringing the control electrode to cathodepotential and permitting a desired high current to energize the X-raytube for producing X-rays. The novel features of my in- 35 vention willbe pointed out with greater particularity in the appended claims.

The accompanying drawing shows in Fig. 1 a side elevation of an X-raytube and a diagram of circuit connections and Fig. 2 is an enlarged lon-40 gitudinal section of the cathode and control electrode assembly.

Referring to the drawing, the X-ray tube 3 is of the thermionic typeoperating with a substantially pure electron discharge as described inU. S. Patent 1,203,495 of W. D. Coolidge. The cathode and controlelectrode structure is shown generally at 4 in Fig. 1. The anode whichis shown at 5 as being of the form commonly used in X-ray tubes and mayconsist of tungsten, or other refractory metal. Its form and structureare not material to this invention. The anode is supported by theWell-known tubular holder assembly 6 which requires no separatedescription.

As shown in Fig. 2 the current emanates from a thermionic filament 1,which is surrounded by a tubular focusing electrode 8. One end of thefilament 1 is connected to a conductor 9, the opposite end beingconnected to the electrode 8 which in turn is connected to the conductorl8. 5 The conductors 9, ID in turn are connected to the conductors II, I2 which are sealed into the glass stem l3. Surrounding this stem is atube I4, also consisting of glass. A cup-shaped control and focusingelectrode l5 surrounds the 10 cathode 1 and the ring-shaped electrode 8.This electrode I5 is mounted by support wires l6, I! on a metal sleevel8 which encircles the tube I 4.

The cathode electrodes 1, 8 are supported from an inner tube l9 by asplit metal tube 20, the wires 15 l0, ID are firmly held in bosses 2l,22. The wire 9 is insulated therefrom by an insulating clamp 23.

The cathode conductors ll, l2 are connected by the conductors 25, 26 tothe low potential secondary of a step-down transformer 21, the primaryof which is connected to the supply mains 28, 29 by the conductors 30,3|. A resistance 30 is provided to regulate the heating current in thecircuit 25, 26.

The capacitor 34 is charged by the high potential secondary of atransformer to which it is connected by the conductors 36, 31 in serieswith a rectifier 38. This rectifier preferably is of the high vacuumthermionic type, such, for example, as described in U. S. Patent1,287,265, of Saul Dushman. The primary of the transformer 35 isconnected'by the conductors 40, 4| in circuit with a switch 42, to themains 28, 29.

In the high potential circuit 33 is an impedance 43, which may assumethe form of an ohmic resistance. The end of the resistance which isconnected to the capacitor 34 also is connectedby the conductor 32 tothe control electrode l5, which surrounds the filament 1. The resistance43 is shunted by the conductors 44, 45, the circuit through which isarranged to be completed by the switch 48. This switch 46 may be of anysu table form for operation in a high voltage circuit, the circuitdiagram merely showing a simple switch closed by pressure upon theinsulated knob 41 against the spring 48.

When the apparatus is operated the resistance 38 is adjusted to a valueat which a desired heating current is obtained in the cathode l, and theswitch 42 is closed, thereby causing the capacitor 34 to be chargedthrough the rectifier 38. If the cathode is heated to its operatingtemperature by energy supplied by the circuit 25, 26 only a. smallcurrent will pass through the X-ray tube as the potential drop in theresistance 43 results in a high enough negative potential upon thecontrol electrode l5 to reduce the space current to a very small value.For example, with an impressed voltage of 85,000 volts and a resistor ofabout 2 megohms used as resistance 43, a current of one tenth of amilliampere will be passed through a 7 given X-ray tube,-(the particularvalue of this current depending on the geometry of the X-ray tube). Acurrent of this magnitude will not produce any substantial X-ray efiect,nor will it discharge the capacitor 34. However, when switch 46 isclosed, short-circuiting the resistance 43, the negaive potential ofcontrol electrode I5 is reduced to zero (with respect to the filament 1)and the capacitor 34 discharges at a high rate. If this capacitor ischosen at a sufiiciently high value a rush of current of the order ofone thousand milliamperes may be produced at a given voltage through theX-ray tube 3 resulting in a high instantaneous output of X-rays. Whenthe switch 46 is again opened high impedance conditions immediatelyreestablish themselves.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An electrical apparatus comprising a thermionic tube which isprovided with a main anode, a maincathode, and an auxiliary electrodesurrounding said cathode whereby current between said main electrodesmay be controlled, a capacitor, electric supply conductors connectedtherefrom to said main electrodes, means for charging said capacitor, anelectric impedance which is included in one of said supply conductorsand having one terminal connected to said cathode, a circuit connectionfrom the opposite terminal of said impedance to said auxiliaryelectrode, and means whereby said impedance may be short-circuited.

2. An electron discharge apparatus adapted for intermittent service forperiods of short duration comprising a thermionic X-ray tube containinga cathode, an anode, and a control electrode which when charged tocathode potential will permit free passage of current through said tubewhile restraining current flow when charged to a higher negativepotential, an electric supply source, conductorsleading from said sourceto said tube, means in circuit with one of said conductors for chargingsaid control electrode to a negative potential with respect to thecathode, discharge conductors connected to said charging means and meansfor connecting said discharge conductors to short-circuit said chargingmeans and permit which is spatially so related to the cathode that flowof current from the cathode occurs with said control electrode atsubstantially cathode potential, electric current conductors connectedto the main electrodes of said tube, an electric capacitor connected tosaid conductors, means for charging said capacitor, an electricresistance included in circuit with one of said conductors which isconnected between said capacitor and the cathode of said tube, a secondconductor connected between said control electrode and a point in saidfirst conductor common to said capacitor and said resistance, conductorsconnected to terminals of said resistance and means for connecting anddisconnecting said last-named conductors.

4. An X-ray installation comprising an X-ray tube having a main cathode,a main anode and a control electrode surrounding said cathode, a sourceof energy, conductors connected to supply energy therefrom to said mainelectrodes, an impedance in circuit with one of said conductors, anelectrical conductor connected to impress a fall of potential in saidimpedance on said control electrode and instantaneously operating meansfor short-circuiting'said impedance at will.

5. An X-ray installation comprising an X-ray tube of the pure electrondischarge type containing an anode, a thermionic cathode, and a controlelectrode surrounding said cathode, an energy supply source, conductorsrespectively connected therefrom to said anode and said cathode, aresistor in circuit with the one of said conductors which is connectedto said cathode, an electric conductor connected between said controlelectrode and said resistor at a point remote from said cathode,conductors connected to the terminals of said resistor, and amanually-controlled switch connected to said last-named conductors.

6. An electrical apparatus comprising a thermionic X-ray tube containinga'main cathode, a main anode and a control electrode which is spatiallyrelated to the cathode to permit flow of current in said tube when atcathode potential, electric supply conductors connected to said maincathode and said main anode, an electric energy source in circuit withsaid supply conductors which is capable of a high rate of discharge, animpedance device in circuit with said energy source and said supplyconductors, another conductor connecting said control electrode to saidmain cathode in series with said impedance device, circuit conductorsconnecting with the respective terminals of said impedance device, and apush-button switch for connecting said circuit conductors in series.

7. An electrical apparatus comprising a thermionic X-ray tube containinga cathode, an anode and a control electrode spatially related to saidcathode to permit free flow of current in said tube when at cathodepotential, an electric energy supply for said anode and cathode which iscapable of a high rate of discharge, conductors leading from said energysupply to said anode, cathode and control electrode respectively, meansin circuit with said control electrode conductor for biasing saidcontrol electrode to a negative potential with respect to said cathodeto restrain free flow of current, and instantaneously-operating meansfor rendering said biasing means ineiiective.

WILLIAM K. KEARSLEY.

